Method for electro-chemical machining turbine wheel in-situ

ABSTRACT

A method for electro-chemical machining (ECM) is provided. Methods may include providing an ECM machine including a controller and a fixture configured for positioning an electrode for ECM, positioning the fixture in a selected dovetail slot of a plurality of dovetail slots in a turbine wheel, the turbine wheel being positioned in-situ in a turbomachine, the fixture positioning the electrode for ECM of a portion of the selected dovetail slot, applying an electrolyte solution between the selected dovetail slot and the electrode, and removing material from the portion of the selected dovetail slot by applying an electric potential to the electrode to create a potential gradient between the electrode and the portion of the selected dovetail slot. The machining may be repeated for each dovetail slot of the turbine wheel in-situ in the turbomachine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending U.S. application Ser. No.______, GE docket number 278675-1, filed on ______.

BACKGROUND OF THE INVENTION

The present invention generally relates to electro-chemical machining(ECM). More particularly, this invention relates to a method ofperforming ECM in-situ of a portion of a dovetail slot, for example,edge regions of slots within turbine wheels employed in turbomachines,including but not limited to gas turbines used in power generation.

In the hostile operating environments of gas turbine engines, thestructural integrity of turbine rotor wheels, buckets, and othercomponents within their turbine sections is of great importance in viewof the high mechanical stresses that the components must be able tocontinuously withstand at high temperatures. For example, the regions ofa turbine wheel forming slots into which the buckets are secured,typically in the form of what are known as dovetail slots, are known toeventually form cracks over time, necessitating monitoring of the wheelin these regions. In some wheel configurations, non-limiting examples ofwhich include the stage 1, 2, and 3 wheels of the General Electric 9FBgas turbine, cooling of the buckets and wheel perimeter is assisted bythe presence of a cooling slot located near the perimeter of the wheeland into which the dovetail slots extend. Over extended periods of timeunder the severe operating conditions of a wheel, cracks may form atcommon edges formed where the dovetail slots and cooling slot intersect.Configuring of the cooling slot geometry to reduce the likelihood ofsuch cracks is desirable in order to improve expected life of a turbinewheel.

While a turbine rotor can be completely disassembled to gain access toits individual wheels, ECM techniques that can be performed with limiteddisassembly are preferred to minimize downtime, such as to fit withinoutage schedules of a gas turbine employed in the power generatingindustry. However, access to the cooling slot is very limited, and anyECM technique must address the difficulty of bringing the tool intostable proximity to the edges being rounded.

Currently, cooling slots of gas turbine engines are generally rounded bymechanical grinding followed by a finishing process, such as BPP (blend,polish, peen). These methods involve using a bit to remove material atthe edge of the cooling slot and then blending and/or polishing theedges to obtain the desired radius of the intersection edges. However, adesired radius is often difficult to achieve if the grinding wasperformed by mechanical means. Furthermore, BPP methods may fail toremove all of the cracks in the cooling slots.

Therefore, it would be desirable if a method existed by which sharpedges prone to cracks on a turbine wheel, particularly edge regions ofslots within the wheel, could be rounded to a desired radius withminimal polishing and/or blending using ECM. It would also be desirableif such a process were able to be performed without necessitatingcomplete disassembly of a turbine rotor to gain access to its individualwheels.

BRIEF DESCRIPTION OF THE INVENTION

A first aspect of the disclosure provides a fixture for anelectro-chemical machining (ECM) electrode, comprising: a clamp having ashape and size configured to selectively engage in at least a portion ofa selected dovetail slot of a plurality of dovetail slots in a turbinewheel; and an electrode mount for positioning an electrode head relativeto the clamp such that the electrode head operatively engages a portionof the selected dovetail slot for electro-chemical machining of theportion.

A second aspect of the disclosure provides a portable electro-chemicalmachining (ECM) cathode for a portion of a selected dovetail slot of aturbine wheel having a plurality of dovetail slots, the ECM cathodecomprising: a cathode body including a cathode head; a clamp having ashape and size configured to selectively engage in at least a portion ofthe selected dovetail slot; and a cathode mount for positioning thecathode head relative to the clamp such that the cathode headoperatively engages the portion of the selected dovetail slot forelectro-chemical machining of the portion.

A third aspect includes a method for electro-chemical machining (ECM),comprising: providing an ECM machine including a controller and afixture configured for positioning an electrode for ECM; positioning thefixture in a selected dovetail slot of a plurality of dovetail slots ina turbine wheel, the turbine wheel being positioned in-situ in aturbomachine, the fixture positioning the electrode for ECM of a portionof the selected dovetail slot; applying an electrolyte solution betweenthe selected dovetail slot and the electrode; and removing material fromthe portion of the selected dovetail slot by applying an electricpotential to the electrode to create a potential gradient between theelectrode and the portion of the selected dovetail slot.

The illustrative aspects of the present disclosure are configured tosolve the problems herein described and/or other problems not discussed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this disclosure will be more readilyunderstood from the following detailed description of the variousaspects of the disclosure taken in conjunction with the accompanyingdrawings that depict various embodiments of the disclosure, in which:

FIG. 1 shows a schematic view of a turbomachine.

FIG. 2 shows an end perspective view of a dovetail slot prior to ECMusing the fixture according to embodiments of the invention.

FIG. 3 shows an end perspective view of the dovetail slot of FIG. 2after machining.

FIG. 4 shows a schematic view of an ECM machine employing a fixture foran ECM electrode according to embodiments of the invention.

FIG. 5 shows a side perspective view of a fixture for an ECM electrodeaccording to embodiments of the invention.

FIG. 6 shows a cross-sectional view of a clamp of the fixture along line6-6 of FIG. 5 while positioned within a selected dovetail slot.

FIG. 7 shows a side perspective view of an illustrative cathode for usethe fixture of FIG. 5.

FIG. 8 shows a side perspective view of the fixture of FIG. 5 with theECM electrode removed.

FIG. 9 shows a top perspective view of the fixture of FIG. 5.

FIG. 10 shows a perspective view of the fixture of FIG. 5 in position toperform ECM on a dovetail slot.

FIG. 11 shows a perspective view of a portable ECM shipping containeraccording to embodiments of the invention.

It is noted that the drawings of the disclosure are not to scale. Thedrawings are intended to depict only typical aspects of the disclosure,and therefore should not be considered as limiting the scope of thedisclosure. In the drawings, like numbering represents like elementsbetween the drawings.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described in terms of fixture 200 (FIG. 5)for an ECM electrode and fixture of an ECM cathode 300 (FIG. 5) formachining at least a portion of a dovetail slot, for example, to repairthe geometry of high stress edge regions thereof that are prone tocracking. Related methods of operation will also be described. Whilevarious applications are foreseeable and possible, applications ofparticular interest include difficult to access regions of components ofgas turbines, including land-based gas turbine engines. Of moreparticular interest are turbine wheels having axial dovetail slots alonga perimeter thereof that are configured for mating with and securingairfoil members to the perimeter of the wheel, and an annular coolingslot that intersects the axial dovetail slots. In this case, the portionof the dovetail slot may include an edge of the cooling slot within thedovetail slot.

As indicated above, the disclosure provides a fixture for an ECMelectrode for a portion of a dovetail slot in a turbine wheel of aturbomachine. FIG. 1 shows a turbomachine 100 that includes a compressorportion 102 operatively coupled to a turbine portion 104 through acommon compressor/turbine shaft 106. Compressor portion 102 is alsofluidically connected to turbine portion 104 through a combustorassembly 108. Combustor assembly 108 includes one or more combustors110. Combustors 110 may be mounted to turbomachine 100 in a wide rangeof configurations including, but not limited to, being arranged in acan-annular array. Compressor portion 102 includes a plurality ofcompressor rotor wheels 112. Rotor wheels 112 include a first stagecompressor rotor wheel 114 having a plurality of first stage compressorrotor blades 116 each having an associated airfoil portion 118.Similarly, turbine portion 104 includes a plurality of turbine rotorwheels 120 (hereafter “turbine wheels”) including a first stage turbinewheel 122 having a plurality of first stage turbine rotor blades 124. Inaccordance with an exemplary embodiment, a fixture 200 for an ECMelectrode 202 (FIG. 5) may be provided for mounting to, for example,first stage turbine wheel 122. It will be understood, however, ECMfixture 200 may be positioned to machine any turbine wheel ofturbomachine 100.

A fragmentary view of a turbine wheel is represented in FIGS. 2-3 andwill serve as an example in the following discussion. As shown in FIG.2, a pair of dovetail slots 130 in a turbine wheel 132 amongst aplurality of dovetail slots in the turbine wheel are illustrated.Dovetail slots 130 may be located in any wheel of turbomachine 100. Asunderstood, dovetail slots 130 are circumferentially spaced about theturbine wheel. Each dovetail slot 130 may take the form of anyblade-to-rotor mounting element now known or later developed. In theexamples illustrated, dovetail slot 130 includes a complex ‘tree’configuration; however, simpler arrangements are possible. For example,dovetail slots 130 may have substantially triangular cross-sections.FIG. 2 depicts two dovetail slots 130 of turbine wheel 132, which isrepresentative of the type conventionally used in gas turbine enginessuch as those used in the power generation industry. An annular coolingslot 134 intersects axial dovetail slots 130. Cooling slot 134 comprisesside edges 136 and radially-outward edges 138. Collectively, edges 136,138 form an edge 140 of cooling slot 134 within dovetail slot 130, i.e.,a slot within a slot. If edges 136 and 138 are sufficiently sharp,cracking can occur in regions of cooling slot 134. As an example,cracking has been observed to occur near the intersection of aft sideedge 136 and radially-outward edge 138 looking downstream of a gasturbine engine (into page as illustrated). Removing turbine wheel 132from the machine for the purpose of repairing the geometries of theseedges 136 and 138 is a long-lead, high-cost operation.

Fixture 200 (FIG. 5) described herein provides a means of repairing thegeometry of turbine wheel 132 in-situ in the case-off condition toreduce stress concentrations, for example, attributable to thegeometries of edge 140, e.g., portions of cooling slot edges 136 and138. As understood, ECM includes applying an AC or DC potential betweenan electrode and the structure to be machined, a current is induced andan electrolyte-based material removal process occurs at the conductiveworkpiece (i.e., anode) when the electrode (i.e., cathode) is negativelycharged in the presence of a conductive fluid (electrolyte solution).Fixture 200 (FIG. 5) may be used to provide an intermediate finishingprocess used in conjunction with other milling and grinding tools, suchas a milling head or an electrochemical chemical grinding (ECG) tool,that are initially used to remove a portion of the dovetail slot, e.g.,an edge of the cooling slot 136 (FIGS. 2-3) within dovetail slot 130.Fixture 200 (FIG. 5) may be employed to continue removing any damagedmaterial and simultaneously rounding mating surfaces that form edges 136and 138 to an improved finishing texture compared to milling or grindingprocesses. Peening may be used in a follow-on operation to apply asurface compression layer. Although the teachings of the invention willbe described relative to the particular setting of revising a portion ofdovetail slot 130 (FIG. 3) in the form of an edge of cooling slot 134within dovetail slot 130, it is emphasized that fixture 200 and theteachings of the invention may be employed for a large number of otherportions within dovetail slots 130 and turbine wheel 132. For example,other portions of dovetail slot 130 may include portions of thedovetail, a root portion of the dovetail slot, etc.

Referring to FIG. 4, a schematic view of an illustrative ECM machine 150employing a fixture 200 (FIG. 5) according to embodiments of theinvention is shown. ECM machine 150 may include an electrolyte solutionsource 152 and electrolyte solution collector 154 for storing liquidelectrolyte prior to and after machining. The electrolyte solution maytake any form now known or later developed for electro-chemicalmachining. Source and collector 152, 154 may include any form of storagecompartment, e.g., plastic or metal tanks ECM machine 150 also includesan ECM control 156 configured to control electric charge supplied to ECMelectrodes engaging a workpiece 158, e.g., turbine wheel 132 (FIG. 3).In one embodiment, workpiece 158 is charged as the anode and fixture 200is configured to position a cathode, as will be described herein. ECMcontrol 156 may include any now known or later developedelectro-chemical machining control system. As understood in the art, ECMcontrol 156 controls a number of attributes such as but not limited to:pump and heater functioning to control a flow rate, pressure,temperature, etc., of an electrolyte solution delivered to workpiece158, the electric charge delivered to the electrodes, etc. ECM machine150 may optionally include a remote control 160 for, for example, remotestart/stop of machining. In one embodiment, ECM machine 150 isconfigured to be portable. For example, all of the parts of ECM machine150 may be configured and sized to be carried within a standard shippingcontainer. In this manner, ECM machine 150 can be employed in the fieldand moved from location to location to service various turbomachines.

Referring to FIG. 5, a perspective view of one embodiment of a fixture200 for an electrode 202 of an ECM machine electrode is illustrated.Fixture 200 may include a clamp 204 having a shape and size configuredto selectively engage in at least a portion of a selected dovetail slot130 (FIG. 2) of a plurality of dovetail slots in turbine wheel 132 (FIG.2). In addition, fixture 200 may include an electrode mount 206 forpositioning an electrode head 208 relative to the clamp such thatelectrode head 208 operatively engages a portion of the selecteddovetail slot 130 for electro-chemical machining of the portion.

Referring to FIGS. 5 and 6, details of an illustrative clamp 204 willnow be described. FIG. 6 shows an enlarged cross-sectional view along6-6 in FIG. 5 of clamp 204 in a selected dovetail slot 130M. Although aparticular form of a clamp will be described relative to FIGS. 5 and 6,the clamp may include any structure having a shape and size configuredto selectively engage in at least a portion of a selected dovetail slot130M (FIG. 6) to hold electrode 202 relative to the slot. As illustratedin FIGS. 5 and 6, in one embodiment, clamp 204 includes an adjustablemember 210 to allow selective securing and removal of the clamp fromselected dovetail slot 130M (FIG. 6). Adjustable member 210 may includeany adjustable member capable of selectively securing the rest of clamp204 within selected mounting dovetail slot 130M (FIG. 6) in turbinewheel 132. For example, clamp 204 may also include a plurality oflongitudinal clamping member(s) 212A, 212B and/or 212C. Adjustablemember 210 adjustably radially displaces at least one of the pluralityof longitudinal clamping members 212A, 212B, 212C, i.e., radiallyrelative to selected dovetail slot 130M, to secure the clamp in selecteddovetail slot 130M. While FIGS. 5 and 6 show three (3) longitudinalclamping members 212A, 212B, 212C, it is understood that two or morethan three segments may also be employed depending, for example, onselected dovetail slot's 130M cross-sectional shape and size. In anyevent, set of adjustable clamping members 212A-C collectively have across-sectional shape to approximately conform with at least a portionof selected dovetail slot 130M. That is, an outer perimeter of members212A-C may approximately conform to at least a portion of the interiorsurface of selected dovetail slot 130M so that when the clamp is axiallyslid into dovetail slot 130M, at least a portion of the clamp engageswith the interior surface of selected dovetail slot 130M to hold theclamp 204 in position relative to selected dovetail slot 130M. In theexample shown, selected dovetail slot 130M has a ‘tree’ dovetailconfiguration, and accordingly, members 212A-C collectively have an atleast similar ‘tree’ dovetail configuration. Clamp 204 may additionallyinclude, for example, one or more projections 216 that engage with theinterior surface of selected dovetail slot 130M when members 212A-C aretightened together with adjustable member 210. Adjustable member 210 mayinclude, for example, one or more set screws, each with a nut seatedwithin an outermost member 212C. Other adjustable members 210 may alsobe employed such as but not limited to screws threaded into members212A-C, adhesives, clamps on the ends of members 212A-C, etc. In anyevent, adjustment of adjustable member 210 may force the one or moreprojections 216 against an inclined surface(s) (adjacent projections216) inside selected dovetail slot 130M to engage projections 216therewith, thus binding clamp 204 to selected dovetail slot 130M andthus preventing movement of electrode 202 (FIG. 5), as will bedescribed. Additional suitable structures for clamping to selecteddovetail slot 130M may include, for example, a vice, spanner, jack, orother equivalent mechanical device connected to electrode mount 206.Clamping members 212A, 212B, 212C may be made of an insulator materialsuch as but not limited to a hard plastic such as nylon orpolytetrafluoroethylene (PTFE). Adjustable member(s) 210 may also bemade out of an insulator material, but could be other materials such asa metal.

Referring to FIGS. 5 and 7-10, details of an example electrode 202 andelectrode mount 206 for positioning electrode head 208 of electrode 202relative to clamp 204 will now be described. FIG. 7 shows a sideperspective view of an illustrative electrode 202 separate fromelectrode mount 206, FIG. 8 shows a side perspective view of fixture 200and electrode mount 206 without an electrode, FIG. 9 shows a plan viewof fixture 200 with electrode mount 206 and electrode 202, and FIG. 10shows fixture 200 in position with a dovetail slot 130M to perform ECM.

Referring to FIG. 7, one embodiment of electrode 202 is illustrated. Itis emphasized that while electrode 202 will be described herein as aparticular shape and size, it may take various forms within the scope ofthe invention. In any event, electrode 202 includes a conductive body216 having an insulator 218 covering the electrode except at an exposedportion 220 of electrode head 208, where conductive body 216 is exposedfor machining. Conductive body 216 may include any conventional or laterdeveloped conductive material used for ECM such as but not limited tosteel, nickel, brass, copper, tungsten, copper tungsten alloy, titanium,etc. As understood, electrode head 208 and, in particular, exposedportion 220 have the shape and size of the feature, attribute to bemachined into the workpiece, e.g., turbine wheel 132 (FIG. 3). Electrode202 may also include electrode head 208 having an opening 222 at an endthereof, which may be in fluid communication with an electrolytesolution passage 224 extending through electrode 208. As shown in FIG.7, electrolyte solution passage 224 (shown in phantom) may be in fluidcommunication, via a conduit 226, with an electrolyte solution source152 (FIG. 4) via ECM control 156 (FIG. 4). In addition thereto or as analternative, as shown best in FIG. 8, clamp 204 may include anelectrolyte solution passage 250 extending through the clamp andterminating adjacent to electrode head 208. Passage 250 may pass throughone or more clamp members 212A, 212B, 212C and terminate, for example,within first aperture 240. During operation, an electrolyte solution maybe provided via conduit 226 to electrode head 208 by opening 222 whileexposed (conductive) portion 220 machines turbine wheel 132 (FIG. 3). Inthe example shown, electrode 202 is substantially linear and electrodehead 208 is substantially rounded. It is understood that electrode head208 may have any shape desired to match the shape to be machined intoturbine wheel 132 (FIG. 3). For example, electrode head 208 may be moreor less rounded, squared off, pointed, etc., depending on the desiredshape in turbine wheel 132 (FIG. 3). In the instant case, as shown inFIG. 3, slot 140 is to have a rounded surface so as to relieve stressamongst edges 136 and 138 (FIGS. 2 and 3), so electrode head 208 has arounded configuration for rendering edge 140 smoother by ECM. Conductivebody 216 may have a shape other than linear such as curved. In anyevent, electrode 208, via conductive body 216, is operatively coupled toECM control 156 (FIG. 4), e.g., by a wire 228 and any necessarycouplings 230 such as a conductive stud 232. In this fashion, wire 228carries an electric charge from ECM control 156 (FIG. 4) to electrode202.

As noted above, electrode mount 206 positions electrode head 208 suchthat electrode head 208 operatively engages a portion, e.g., edge 140(FIG. 3), of selected dovetail slot 130M (FIG. 6) for electro-chemicalmachining of a portion of the slot. Electrode mount 206 may include anystructure capable of positioning electrode head 208 relative to theportion of selected dovetail slot 130M. As understood in the art, anelectrode head 208 of an ECM machine must be in close proximity to aworkpiece such as a dovetail slot 130. In one example, electrode head208 may be approximately 1-30 microns and is typically about 10 micronsfrom edge 140, and charged negative as a cathode by wire 228 whileturbine wheel 132 (FIGS. 2-3) is charged positive as an anode using awire 230 (see FIG. 4). In one embodiment, as illustrated, electrodemount 206 may include a first aperture 240 (FIGS. 8 and 9) extendingthrough a section of clamp 204. In the example shown, since edge 140(FIG. 3) is close to a lowermost, root section 142 (FIGS. 3 and 6) ofselected dovetail slot 130M, the section of clamp 204 includes alowermost clamping member 212C. However, first aperture 240 may extendthrough any clamp member or members 212A-C. If necessary, and asillustrated, first aperture 240 may extend at an angle relative to alongitudinal axis of clamp 204, and consequently selected dovetail slot130M, to position electrode head 208 at the desired position. The anglemay be any angle necessary to place electrode head 208 in an appropriateposition for ECM. As shown in FIG. 9, electrode mount 206 may furtherinclude a positioning member 242 coupled to an end of clamp 204.Positioning member 242 may include a second aperture 244 extendingthrough the positioning member and substantially aligned with firstaperture 240. Electrode 202 may extend through both apertures 240, 244.In this fashion, positioning member 242 may provide additional supportof electrode 202. Positioning member 242 may be made of the samematerial as clamp 204, and may be coupled to clamp 204 in any fashion,e.g., adhesives, fasteners such as screws, etc.

Referring to FIGS. 7 and 8, as described, electrode head 208 may includeopening 222 at an end thereof, which may be in fluid communication withelectrolyte solution passage 224 extending through electrode 202, i.e.,conductive body 216. As shown best in FIG. 8, in addition thereto or asan alternative, clamp 204 may also include an electrolyte solutionpassage 250 (shown in phantom) extending through the clamp andterminating adjacent to electrode head 208. In one example, passage 250may terminate in first aperture 240. However, passage 250 may alsoterminate, for example, at any location capable of delivering theelectrolyte solution to the machining location. For example, passage 250could terminate at an outer surface of clamp member(s) 212A-C adjacentelectrode head 208. Electrolyte solution passage 250 may be in fluidcommunication, via a conduit 252, with an electrolyte solution source152 (FIG. 4) via ECM control 156 (FIG. 4).

As noted herein, electrode 202 may take the form of a cathode andturbine wheel 132 may be charged as an anode by ECM control 156 (FIG.4). Accordingly, as shown in FIGS. 5 and 9, aspects of the invention mayalso include an ECM cathode 300 for a portion of selected dovetail slot130M (FIG. 3) of turbine wheel 132 (FIG. 3) having a plurality ofdovetail slots 130 (FIG. 3). In this case, ECM cathode 300 may includecathode 302 including cathode head 308. As described herein, clamp 204may have a shape and size configured to selectively engage in at least aportion of the selected dovetail slot 130M (FIG. 6). Electrode mount 206may act as a cathode mount to position cathode head 208 relative toclamp 204 such that the cathode head operatively engages the portion ofthe selected dovetail slot for electro-chemical machining of theportion.

In operation, ECM machine 150 is provided with controller 156 andfixture 200 configured for positioning electrode 202 for ECM. As shownin FIG. 6, fixture 200 is then positioned in selected dovetail slot 130Mof plurality of dovetail slots 130 in turbine wheel 132, which isin-situ in turbomachine 100. That is, clamp 204 is slid into a selecteddovetail slot 130M, as shown in FIG. 6. Adjustable members 210 areadjusted to securely fasten clamp 204 in selected dovetail slot 130M(FIG. 6). Clamp 204 and insulator 218 of electrode 202 insulateconductive body 216 such that only exposed portion 220 acts to provideelectro-chemical machining. Electrode 202 may be positioned within firstaperture 240 of electrode mount 206 or later inserted such thatelectrode head 208 is in close proximity to a portion of slot 130M suchas edge 140 (FIG. 3). Positioning member 242 may be employed withelectrode mount 206 or omitted if first aperture 240 provides sufficientsupport. FIG. 10 shows fixture 200, 300 in position within a selecteddovetail slot 130M. An electrolyte solution is then applied betweenselected dovetail slot 130M and electrode 200, e.g., via conduit 226(FIG. 7) to electrode head 208 (FIGS. 7, 8), or by conduit 252 (FIG. 8)and passage 250 (FIG. 8). That is, ECM control 156 acts to provideelectrolyte solution by conduit(s) 226 (FIG. 7) and/or 252 (FIG. 8),e.g., by a pump. Electrolyte solution may be heated to any desiredtemperature and provided at a desired flow rate and pressure by ECM 156in a known fashion. In operation, electrolyte solution is supplied toelectrode head 208 by ECM control 156 at a specified, temperature, flowrate, pressure, etc.

As noted, electrode 202 includes a conductive body 216 that iselectrically coupled to ECM control 156 (FIG. 4) by wire 228. Similarly,turbine wheel 132 is electrically coupled to ECM control 156 (FIG. 4) toact as an anode by wire 230 (FIG. 4). Material is removed from theportion of selected dovetail slot 130M by applying an electric potentialto electrode 202 to create a potential gradient between electrode 202and the portion of slot 130M. That is, electrode head 208 (cathode) andturbine wheel 132 (anode) are appropriately charged so that electrodehead 208 electro-chemically machines edge 140, radiusing it out andsmoothing it. As illustrated, the ECM occurs within dovetail slot 130Mand an operator cannot see the actual machining occurring, i.e., fixture200 visually obstructs the ECM in the selected dovetail slot.

ECM according to embodiments of the invention may be performed afterother initial machining such as milling, grinding and/or de-burring edge140. Once one dovetail is completed, the fixture may be removed andpositioned into another dovetail slot and the process repeated for eachdovetail slot 130, as necessary. Fixture 200 (cathode 300) thus providea portable mechanism to provide precise ECM to a portion of turbinewheel 132 in the field and in-situ. That is, turbine wheel 132 is notremoved from turbomachine 100, thus reducing the costs of removing andtransporting a turbine wheel for repair. Hence, fixture 200 (cathode300) may be employed to remove a precise amount of material that isprone to cracking in a turbine wheel 132 (FIG. 3) in-situ, reducing thetime and costs of removing turbine wheel 132 (FIGS. 2-3) fromturbomachine 100 (FIG. 1). The surface finish may be mirror finish,e.g., having a surface roughness (Ra) of about 0.025-0.25 microns.

In addition, fixture 200 may be moved from site-to-site with ECM machine150 (FIG. 5) in a portable manner, allowing use in a wide variety oflocations. As noted herein, ECM machine 150 (FIG. 5) may be configuredto be portable. For example, as shown in FIG. 11, all of the parts ofECM machine 150 may be configured and sized to be carried within astandard shipping container 400. Container 400 may include anyconventional shipping container. Here, however, container 400 mayinclude ECM machine 150 having electrolyte solution source 152 andelectrolyte solution collector 154 for storing liquid electrolytesolution prior to and after machining. Source and collector 152, 154 mayinclude any form of storage compartment, e.g., plastic or metal tanks,and may include any necessary heating, cooling and/or filtering systemsfor the electrolyte solution. ECM control 156 may also be provided tocontrol electric charge supplied to ECM electrodes. As noted, ECMcontrol 156 may include any now known or later developedelectro-chemical machining control system, and may include touch panelcontrols 402. As understood in the art, ECM control 156 controls anumber of attributes such as but not limited to: pump and heaterfunctioning to control a flow rate, pressure, temperature, etc., of anelectrolyte solution, the electric charge delivered to the electrodes,etc. Container 400 may include a removable floor 404 for systemmaintenance or shop applications, and may include any necessary externaldisconnect panel(s) 406 for quick connect field leads. In addition,container 400 may include any necessary climate controls, any necessarycable runs for placement of at least parts of ECM machine 150 outside ofthe container. In this manner, ECM machine 150 can be employed in thefield and moved from location to location to service variousturbomachines

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. The corresponding structures,materials, acts, and equivalents of all means or step plus functionelements in the claims below are intended to include any structure,material, or act for performing the function in combination with otherclaimed elements as specifically claimed. The description of the presentdisclosure has been presented for purposes of illustration anddescription, but is not intended to be exhaustive or limited to thedisclosure in the form disclosed. Many modifications and variations willbe apparent to those of ordinary skill in the art without departing fromthe scope and spirit of the disclosure. The embodiment was chosen anddescribed in order to best explain the principles of the disclosure andthe practical application, and to enable others of ordinary skill in theart to understand the disclosure for various embodiments with variousmodifications as are suited to the particular use contemplated.

What is claimed is:
 1. A method for electro-chemical machining (ECM),comprising: providing an ECM machine including a controller and afixture configured for positioning an electrode for ECM; positioning thefixture in a selected dovetail slot of a plurality of dovetail slots ina turbine wheel, the turbine wheel being positioned in-situ in aturbomachine, the fixture positioning the electrode for ECM of a portionof the selected dovetail slot; applying an electrolyte solution betweenthe selected dovetail slot and the electrode; and removing material fromthe portion of the selected dovetail slot by applying an electricpotential to the electrode to create a potential gradient between theelectrode and the portion of the selected dovetail slot.
 2. The methodof claim 1, further comprising: removing the fixture from the selecteddovetail slot; and repeating the positioning, applying and the removingfor each dovetail slot of the plurality of dovetail slots.
 3. The methodof claim 1, wherein the fixture visually obstructs the ECM in theselected dovetail slot.
 4. The method of claim 1, wherein the portion ofthe selected dovetail slot includes an edge of a cooling slot within theselected dovetail slot.